The objective of this proposal is to develop a technique for labeling antibodies with metallic radionuclides and to determine the relationship between accelerated blood clearance (caused by increased chelating groups per antibody) and the retention of immunology activity. In preliminary studies we found that the use of monomer albumin, the use of a conjugation method that assures a single type of linkage, and purification of the radiolabeled substrate did not prevent accelerated plasma clearance. The major factor controlling plasma clearance appeared to be the level of conjugation per antibody molecule. Thus we propose to study the effect of various reaction conditions including the conjugation method to determine if our approach to produce better tumor imaging agents by balancing altered substrate specificity caused by modification against accelerated plasma clearance is valid. If successful, this methodology will allow not only increased specificity in tumor detection because of the retention of immunologic activity but also a method to permit the use of earlier imaging times and consequently better radionuclides than presently employed with the agent of choice Ga-67 citrate.